The present invention relates to a cooling system for an engine, and particularly for an automotive engine.
Generally, in the cooling system, the coolant is circulated from a water pump passing through water jackets of an engine and a radiator when a thermostat valve opens. In a conventional cooling system for an automotive engine, a thermostat is disposed in a coolant passage near an outlet of water jackets of the engine. Such a system is disclosed in Japanese Utility Model Application Laid Open No. 57-83225. Further, there has been a cooling system in which a thermostat is disposed in a coolant passage near an inlet of a water pump.
However, in the former system, when the temperature of coolant in the engine reaches a predetermined opening temperature of the thermostat, the thermostat valve opens immediately. Since the low temperature coolant from a radiator flows into the water jackets, the temperature of coolant in the water jackets is rapidly lowered to decrease the temperature of the engine. The thermostat senses the decrease of the temperature of coolant at the outlet position of the water jackets and the thermostat valve is closed. Thus, the temperature of coolant in the water jackets is remarkably changed by the operations of the thermostat. Such a rapid variation of coolant temperature affects the engine.
In the latter system, since a thermo-sensitive device of the thermostat is disposed upstream of the water pump, temperature of the coolant entering into the water jackets is controlled to a constant value. However, the thermostat has a large conduit resistance, so that the efficiency of the water pump is reduced. In order to improve the efficiency of the pump, the thermostat and water pump should be made large in size and capacity. Further, when the water pump is driven at high speed, the pressure in the passage between the thermostat and the water pump becomes low because of the large conduit resistance, so that cavitation occurs in the water pump.
Accordingly, it is preferable to dispose a thermo-sensitive device at the inlet of the water pump so as to sense the temperature of the coolant at an inlet side of the water pump and to dispose a valve device at the outlet of water jackets of the engine, so that the above described disadvantages in the prior art may be eliminated.